Corporation Tax Deadlines & Penalties: The Complete Guide for 2026

Every limited company registered in the UK must file a corporation tax return (CT600) with HMRC and annual accounts with Companies House — even if the company is dormant or made a loss. Missing these deadlines doesn't just risk a fine; it can trigger automatic penalties, daily interest charges, and even strike-off proceedings.

Understanding exactly when your deadlines fall and what happens if you miss them is the single most important thing a company director can do to stay compliant. This guide covers every deadline, every penalty tier, and practical steps to make sure you never file late.

Many directors confuse the two filing requirements, or assume they are the same thing. They are not.

1. HMRC — CT600 Corporation Tax Return

This is your tax return. It tells HMRC how much profit your company made, what tax reliefs apply, and how much corporation tax is due. You must file it within 12 months of the end of your accounting period.

2. Companies House — Annual Accounts

This is your public-facing financial statement. It shows your balance sheet, and for non-micro companies, a profit and loss account. You must file it within 9 months of the end of your financial year (for private limited companies).

Critically, the payment deadline for corporation tax is different from both filing deadlines — tax must be paid within 9 months and 1 day of the end of your accounting period.

For example, if your accounting period ends on 31 March 2026:

• Corporation tax payment due: 1 January 2027
• Companies House accounts due: 31 December 2026
• CT600 return due to HMRC: 31 March 2027

HMRC operates a tiered penalty system for late CT600 returns. The penalties escalate the longer you delay:

• 1 day late — £100 automatic penalty
• 3 months late — Another £100 penalty (total £200)
• 6 months late — HMRC estimates your tax bill and adds a penalty of 10% of the unpaid tax
• 12 months late — A further 10% of the unpaid tax is added

These penalties apply per return, so if you have two overdue returns for consecutive accounting periods, the penalties double.

On top of penalties, HMRC charges late payment interest on any corporation tax paid after the 9-month-and-1-day deadline. The interest rate is set by HMRC and is currently 7.25% per annum — significantly higher than most savings accounts.

Important: even if your company made no profit and owes zero tax, you will still receive the flat-rate penalties for filing the CT600 late.

Companies House penalties are separate from HMRC and are non-negotiable — there is no appeal process based on reasonable excuse.

For a private limited company, the penalties are:

• Up to 1 month late: £150
• 1 to 3 months late: £375
• 3 to 6 months late: £750
• More than 6 months late: £1,500

If your accounts were also filed late the previous year, these penalties are doubled:

• Up to 1 month late: £300
• 1 to 3 months late: £750
• 3 to 6 months late: £1,500
• More than 6 months late: £3,000

Companies House is strict about enforcement. Penalties are issued automatically and directors are personally liable. If accounts remain unfiled, Companies House may begin strike-off proceedings, which can dissolve your company entirely.

A common misconception is that dormant companies don't need to file. This is wrong.

Even if your company has had no transactions whatsoever, you must still:

• File dormant accounts with Companies House (AA02 form or abbreviated accounts)
• File a CT600 return with HMRC (you can notify HMRC the company is dormant, but the first return must still be filed)

The same penalty regimes apply to dormant companies. The good news is that dormant filings are straightforward — the balance sheet simply shows share capital and no activity.

With WeFile, dormant company filings take just a few minutes. Our wizard auto-detects dormant status and pre-fills the required fields.

Your deadlines are based on your accounting reference date (ARD), which is typically the last day of the month in which your company's financial year ends.

You can find your ARD on Companies House by searching for your company. It's listed under "Accounts" on your company overview page.

Once you know your ARD, the deadlines are:

• Companies House: ARD + 9 months (e.g., ARD 31 March → deadline 31 December)
• HMRC CT600: ARD + 12 months
• Tax payment: ARD + 9 months + 1 day

WeFile automatically calculates all of these dates for you. When you add a company to your WeFile account using your company number, we fetch your filing periods directly from Companies House and show you exactly which periods need filing and when they're due.

Don't panic — but do act quickly. The penalty tiers mean that every day counts, especially around the 1-month and 3-month thresholds.

Here's what to do:

Step 1: File as soon as possible

The penalties stop escalating once your filing is received and accepted. Filing today rather than next week could save you hundreds of pounds.

Step 2: Pay any corporation tax owed

Interest is calculated daily, so paying promptly reduces the total charge.

Step 3: Check if you can appeal

HMRC allows appeals for late filing penalties if you have a "reasonable excuse" — such as serious illness, bereavement, or a natural disaster. Companies House does not accept reasonable excuse appeals for late filing penalties.

Step 4: Set up reminders for next year

The best way to avoid penalties is to never miss a deadline in the first place. WeFile sends you automatic reminders when your filing periods are approaching.

File early. You don't have to wait until the deadline approaches. You can file your accounts and CT600 as soon as your accounting period ends. Filing early gives you a buffer for any issues.

Keep your records up to date. If your bookkeeping is done monthly, preparing your year-end figures takes hours, not weeks. Consider using accounting software like Xero, QuickBooks, or FreeAgent — all of which integrate directly with WeFile.

Use WeFile's filing wizard. Our step-by-step process guides you through the entire CT600 and Companies House filing. Corporation tax is calculated automatically, and you can review everything before submitting.

Set up a team. If you manage filings for multiple companies, WeFile's team feature lets you invite colleagues and delegate filing tasks without sharing login credentials.

Check your filing status. After submitting, WeFile tracks your submission status in real time. You'll receive a confirmation email once both HMRC and Companies House have accepted your return.

WeFile makes corporation tax filing simple, affordable, and fast. Whether you're filing for a single dormant company or managing dozens of active businesses, our platform handles the complexity so you don't have to.

Ready to file? Create your free account at wefile.co.uk and submit your CT600 and Companies House accounts in minutes — no accountancy knowledge required.

If you have any questions, reach out to our support team or ask in the WeFile Community Forum. We're here to help.